Most ultrasonic flow measurements seek to leverage information contained in fluid borne disturbances of a specific temporal frequency. The specific frequency often results from natural frequencies of the drive electronics, the transducer, or the resonant transmission characteristic of the pipe wall.
Referring to FIG. 8, one of the primary challenges associated with clamp-on ultrasonic flow metering is the interference between the structural borne ultrasonic signal component 100 and the desired fluid borne ultrasonic signal component 102. The structural borne component 100 of the ultrasonic signal is often of the same or similar frequency and essentially masks the fluid borne component 102 of the ultrasonic signal.
Standard pipes are fairly effective waveguides for structural borne acoustics components 100. The ultrasonic pulse propagates along the wall of a pipe 104 with very little damping and rings around the circumference numerous times until the inherent damping in the pipe and the propagation of energy axially away from the initial excitation eventually dissipates the structural borne ultrasonic waves.